Method for operating a washing machine appliance

ABSTRACT

A method for operating a washing machine appliance is provided. The method includes determining a power delivered to a motor of the washing machine appliance while an angular velocity of a drum of the washing machine appliance is increasing. The method also includes establishing a slope of the power delivered to the motor. The slope of the power delivered to the motor is monitored in order to establish if the slope of the power delivered to the motor exceeds a threshold value.

FIELD OF THE INVENTION

The present subject matter relates generally to washing machine appliances and methods for operating the same.

BACKGROUND OF THE INVENTION

Washing machine appliances generally include a tub with a drum rotatably mounted therein. The drum defines a wash chamber for receiving articles for washing. During operation of washing machine appliances, wash fluid is directed into the tub and onto articles within the wash chamber of the drum. The motor can rotate the drum at various speeds to agitate articles within the wash chamber in wash fluid, to wring wash fluid from articles within the wash chamber, etc.

The motor can rotate the drum at high speeds during operation of the washing machine appliances. For example, during certain cycles, the motor can rotate the drum at speeds exceeding one thousand revolutions per minute. When the drum is rotating as such high speeds, the drum or a connecting shaft can flex causing the drum to strike the tub. In particular, the drum can strike the tub when an imbalanced load of articles is disposed within the drum. When the drum strikes the tub, the washing machine appliance can be damaged. For example, the drum can gouge the tub when it strikes the tub while rotating at high speeds.

Accordingly, a washing machine appliance with features for detecting a drum of the washing machine appliance striking a tub of the washing machine appliance would be useful. In particular, a washing machine appliance with features for detecting a drum of the washing machine appliance striking a tub of the washing machine appliance without an additional sensor would be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present subject matter provides a method for operating a washing machine appliance. The method includes determining a power delivered to a motor of the washing machine appliance while an angular velocity of a drum of the washing machine appliance is increasing and also includes establishing a slope of the power delivered to the motor. The slope of the power delivered to the motor is monitored in order to establish if the slope of the power delivered to the motor exceeds a threshold value, indicating that the basket may be striking the tub. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In a first exemplary embodiment, a method for operating a washing machine appliance is provided. The washing machine has a drum rotatably mounted within a tub. The washing machine appliance also has a motor configured for selectively rotating the drum within the tub. The method comprises rotating the drum at a first angular velocity with the motor, determining a power delivered to the motor at the step of rotating the drum at the first angular velocity, rotating the drum at a second angular velocity with the motor, determining the power delivered to the motor at the step of rotating the drum at the second angular velocity, calculating a change in the power delivered to the motor over time based at least in part on the power delivered to the motor at the step of rotating the drum at the first angular velocity and the power delivered to the motor at the step of rotating the drum at the second angular velocity, and establishing whether the change in the power delivered to the motor over time exceeds a threshold value.

In a second exemplary embodiment, a method for operating a washing machine appliance is provided. The washing machine has a drum rotatably mounted within a tub. The washing machine appliance also has a motor configured for selectively rotating the drum within the tub. The method includes spinning the drum with the motor, increasing an angular velocity of the drum at a first acceleration rate during the step of spinning, increasing the angular velocity of the drum at a second acceleration rate after the step of increasing the angular velocity of the drum at the first acceleration rate, determining an average power delivered to the motor during the step of increasing the angular velocity of the drum at the second acceleration rate, establishing a slope of the average power delivered to the motor, and monitoring the slope of the average power delivered to the motor in order to establish if the slope of the average power delivered to the motor exceeds a threshold value.

In a third exemplary embodiment, a washing machine appliance is provided. The washing machine appliance includes a cabinet, a tub positioned within the cabinet and a drum rotatably mounted within the tub. The drum defines a wash chamber for receipt of articles for washing. A motor is in mechanical communication with the drum. The motor is configured for selectively rotating the drum within the tub. A controller is in operative communication with the motor. The controller is configured for rotating the drum at a first angular velocity with the motor, determining a power delivered to the motor at the step of rotating the drum at the first angular velocity, rotating the drum at a second angular velocity with the motor, determining the power delivered to the motor at said step of rotating the drum at the second angular velocity, calculating a change in the power delivered to the motor over time based at least in part on the power delivered to the motor at the step of rotating the drum at the first angular velocity and the power delivered to the motor at the step of rotating the drum at the second angular velocity, and establishing whether the change in the power delivered to the motor over time exceeds a threshold value.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures.

FIG. 1 provides a front, elevation view of a washing machine appliance according to an exemplary embodiment of the present subject matter;

FIG. 2 illustrates a side, section view of the exemplary washing machine appliance of FIG. 1.

FIG. 3 illustrates a method for operating a washing machine appliance according to an exemplary embodiment of the present subject matter.

FIG. 4 illustrates plots of wash cycles with fault and no fault loads.

FIG. 5 illustrates a method for operating a washing machine appliance according to another exemplary embodiment of the present subject matter.

FIG. 6 illustrates a method for operating a washing machine appliance according to an additional exemplary embodiment of the present subject matter.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 provides a front, elevation view of an exemplary horizontal axis washing machine appliance 100. FIG. 2 provides a side, section view of washing machine appliance 100. As may be seen in FIG. 1, washing machine appliance 100 includes a cabinet 102 that extends between a top portion 103 and a bottom portion 105, e.g., along a vertical direction. Cabinet 102 also includes a front panel 104. A door 112 is mounted to front panel 104 and is rotatable about a hinge (not shown) between an open position facilitating access to a wash drum or basket 120 (FIG. 2) located within cabinet 102, and a closed position (shown in FIG. 1) hindering access to basket 120. A user may pull on a handle 113 in order to adjust door 112 between the open position and the closed position.

A control panel 108 including a plurality of input selectors 110 is coupled to front panel 104. Control panel 108 and input selectors 110 collectively form a user interface input for operator selection of machine cycles and features. For example, in one embodiment, a display 111 indicates selected features, a countdown timer, and/or other items of interest to machine users.

Referring now to FIG. 2, a tub 114 defines a wash compartment 119 configured for receipt of a washing fluid. Thus, tub 114 is configured for containing washing fluid, e.g., during operation of washing machine appliance 100. Washing fluid disposed within tub 114 may include at least one of water, fabric softener, bleach, and detergent. Tub 114 includes a back wall 116 and a sidewall 118 and also extends between a top 115 and a bottom 117, e.g., along the vertical direction.

Basket 120 is rotatably mounted within tub 114 in a spaced apart relationship from tub sidewall 118 and the tub back wall 116. Basket 120 defines a wash chamber 121 and an opening 122. Opening 122 of basket 120 permits access to wash chamber 121 of basket 120, e.g., in order to load articles into basket 120 and remove articles from basket 120. Basket 120 also defines a plurality of perforations 124 to facilitate fluid communication between an interior of basket 120 and tub 114. A sump 107 is defined by tub 114 and is configured for receipt of washing fluid during operation of appliance 100. For example, during operation of appliance 100, washing fluid may be urged by gravity from basket 120 to sump 107 through plurality of perforations 124.

A spout 130 is configured for directing a flow of fluid into tub 114. Spout 130 may be in fluid communication with a water supply (not shown) in order to direct fluid (e.g., clean water) into tub 114. A pump assembly 150 (shown schematically in FIG. 2) is located beneath tub 114 for draining tub 114 of fluid. Pump assembly 150 is in fluid communication with sump 107 of tub 114 via a conduit 170. Thus, conduit 170 directs fluid from tub 114 to pump assembly 150. Pump assembly 150 is also in fluid communication with a drain 140 via piping 174. Pump assembly 150 can urge fluid disposed in sump 107 to drain 140 during operation of appliance 100 in order to remove fluid from tub 114. Fluid received by drain 140 from pump assembly 150 is directed out of appliance 100, e.g., to a sewer or septic system.

In addition, pump assembly 150 is configured for recirculating washing fluid within tub 114. Thus, pump assembly 150 is configured for urging fluid from sump 107, e.g., to spout 130. For example, pump assembly 150 may urge washing fluid in sump 107 to spout 130 via hose 176 during operation of appliance 100 in order to assist in cleaning articles disposed in basket 120. It should be understood that conduit 170, piping 174, and hose 176 may be constructed of any suitable mechanism for directing fluid, e.g., a pipe, duct, conduit, hose, or tube, and are not limited to any particular type of mechanism.

A motor 128 is in mechanical communication with basket 120 in order to selectively rotate basket 120, e.g., during an agitation or a rinse cycle of washing machine appliance 100 as described below. Ribs 126 extend from basket 120 into wash compartment 119. Ribs 126 assist agitation of articles disposed within wash compartment 119 during operation of washing machine appliance 100. For example, ribs 126 may lift articles disposed in basket 120 during rotation of basket 120.

A drawer 109 is slideably mounted within front panel 104. Drawer 109 receives a fluid additive (e.g., detergent, fabric softener, bleach, or any other suitable liquid) and directs the fluid additive to wash compartment 119 during operation of washing machine appliance 100. Additionally, a reservoir 160 is disposed within cabinet 102. Reservoir 160 is also configured for receipt of fluid additive for use during operation of washing machine appliance 100 (shown in FIG. 1). Reservoir 160 is sized such that a volume of fluid additive sufficient for a plurality or multitude of wash cycles of washing machine appliance 100 may fill reservoir 160. Thus, for example, a user can fill reservoir 160 with fluid additive and operate washing machine appliance 100 for a plurality of wash cycles without refilling reservoir 160 with fluid additive. A reservoir pump 162 is configured for selective delivery of the fluid additive from reservoir 160 to tub 114.

Operation of washing machine appliance 100 is controlled by a processing device or controller 180 that is operatively coupled to control panel 108 for user manipulation to select washing machine cycles and features. In response to user manipulation of control panel 108, controller 180 operates the various components of washing machine appliance 100 to execute selected machine cycles and features.

Controller 180 may include a memory and microprocessor, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with a cleaning cycle. The memory may represent random access memory such as DRAM, or read only memory such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor. Alternatively, controller 180 may be constructed without using a microprocessor, e.g., using a combination of discrete analog and/or digital logic circuitry (such as switches, amplifiers, integrators, comparators, flip-flops, AND gates, and the like) to perform control functionality instead of relying upon software. Control panel 58 and other components of washing machine appliance 50 may be in communication with controller 180 via one or more signal lines or shared communication busses.

Controller 180 is in operative communication with motor 128. Thus, controller 180 can selectively activate and operate motor 128, e.g., depending upon a wash cycle selected by a user of washing machine appliance 100. Controller 180 is also configured for monitoring a power delivered to motor 128. As will be understood by those skilled in the art, power delivered to motor 128 can be measured or determined by controller 180 utilizing various methods. As an example, controller 180 or motor 128 may include a power measurement circuit. In alternative exemplary embodiments, controller 180 may monitor the power delivered to motor 128 utilizing any other suitable mechanism or method.

In an illustrative example of operation of washing machine appliance 100, laundry items are loaded into basket 120, and washing operation is initiated through operator manipulation of input selectors 110. Tub 114 is filled with water and detergent to form a wash fluid. One or more valves (not shown) can be actuated by controller 180 to provide for filling tub 114 to the appropriate level for the amount of articles being washed. Once tub 114 is properly filled with wash fluid, the contents of basket 120 are agitated with ribs 126 for cleansing of laundry items in basket 120.

After the agitation phase of the wash cycle is completed, tub 114 is drained. Laundry articles can then be rinsed by again adding wash fluid to tub 114, depending on the particulars of the cleaning cycle selected by a user, ribs 126 may again provide agitation within wash compartment 119. One or more spin cycles may also be used. In particular, a spin cycle may be applied after the wash cycle and/or after the rinse cycle in order to wring wash fluid from the articles being washed. During a spin cycle, basket 120 is rotated at relatively high speeds.

While described in the context of a specific embodiment of horizontal axis washing machine appliance 100, using the teachings disclosed herein it will be understood that horizontal axis washing machine appliance 100 is provided by way of example only. Other washing machine appliances having different configurations, different appearances, and/or different features may also be utilized with the present subject matter as well, e.g., vertical axis washing machine appliances.

FIG. 3 illustrates a method 300 for operating a washing machine appliance according to an exemplary embodiment of the present subject matter. Method 300 can be used to operate any suitable washing machine appliance, such as washing machine appliance 100 (FIG. 1). Controller 180 of washing machine appliance 100 may be programmed or utilized to implement method 300. As discussed in greater detail below, method 300 can assist with detecting striking of tub 114 with basket 120 during rotation of basket 120 within tub 114.

Prior to step 310, controller 180 can operate motor 128 such that motor 128 spins or rotates basket 120. In particular, controller 180 can operate motor 128 such that motor 128 accelerates basket 120 and an angular velocity of basket 120 is increasing. As an example, when motor 128 is spinning basket 120 at a speed exceeding a threshold speed, e.g., about nine hundred revolutions per minute or about one thousand revolutions per minute, controller 180 can operate motor 128 to accelerate basket 120 at a particular acceleration rate, e.g., about two revolutions per minute per second. The particular acceleration rate can be selected in order permit or assist controller 180 with detecting changes in power delivered to motor 128 as discussed in greater detail below.

At step 310, controller 180 calculates or determines a filtered power delivered to motor 128, e.g., when motor 128 is rotating basket 120 above the threshold speed described above. By filtering the power calculation or determination at step 310, controller 180 can reduce noise within the power signal and avoid false failure detections during method 300. As an example, at step 310, controller 180 can calculate or determine an average power delivered to motor 128, such as a rolling average power delivered to motor 128 during a time interval or window. The window can be any suitable time interval. For example, the window may be about eight seconds.

At step 320, controller 180 calculates a slope of the filtered power delivered to motor 128 over time, e.g., during the window. As an example, at step 320, controller 180 can calculate or determine a first derivative of the rolling average power delivered to motor 128 during the window with respect to time.

As will be understood by those skilled in the art, controller 180 can set or configure motor 128 to operate at a target speed, and motor 128 will accelerate to the target speed. As an example, controller 180 can set the target speed of motor 128 to value above one thousand revolutions per minute, such as about one thousand two hundred and fifty revolutions per minute. Controller 180 can operate motor 128 such that a driving speed of motor 128, e.g., continuously or constantly, increases to the target speed of motor 128 during a time interval. In particular, controller 180 can monitor an actual speed of basket 120 and increase or decrease power delivered or supplied to motor 128 in order to increase or decrease the actual speed of basket 120 and match the actual speed of basket 120 to the driving speed of motor 128 during the time interval.

At step 330, controller 180 determines whether the driving speed of motor 128 is greater than a threshold speed. The threshold speed can be any particular speed. For example, the threshold speed may be about one thousand revolutions per minute or about nine hundred revolutions per minute. In particular, the threshold speed may be selected such that the threshold speed is a speed above which basket 120 is likely to strike tub 114 during rotation of basket 120 within tub 114. If the driving speed is not greater than the threshold speed at step 330, controller 180 terminates method 300, e.g., because basket 120 is unlikely to strike tub 114. Conversely, controller 180 determines whether the filtered power delivered to motor 128 is greater than a threshold power at step 340 if the driving speed is greater than the threshold speed at step 330.

The threshold power can be any suitable power at step 340. As an example, the threshold power may be about seven hundred Watts. The threshold power can be selected in order permit controller 180 to detect faults or errors during operation of washing machine appliance 100. For example, if the average power delivered to motor 128 is greater than the threshold power at step 340, a clothing article could be lodged between tub 114 and basket 120 such that rotation of basket 120 within tub 114 is hindered. Similar problems can also be detected at step 340 if the average power delivered to motor 128 is greater than the threshold power. Thus, controller 180 can activate a fault mode of washing machine appliance 100 and, e.g., deactivate motor 128 or washing machine appliance 100, at step 380 if the filtered power delivered to motor 128 is greater than the threshold power at step 340. Conversely, controller 180 determines whether a drum speed is greater than the threshold speed at step 350 if the filtered power delivered to motor 128 is not greater than the threshold power at step 340. As an example, controller 180 can measure the speed at which basket 120 is rotating in order to determine the drum speed (e.g., in revolutions per minute) at step 350.

At step 360, controller 180 determines whether the slope of the filtered power delivered to motor 128 is greater than a threshold value if the drum speed is greater than the threshold speed at step 350. The threshold value can be any suitable value at step 360. In particular, the threshold value can be selected in order permit controller 180 to detect basket 120 rubbing or striking tub 114 during rotation of basket 120 within tub 114. For example, if the slope of the average power delivered to motor 128 is greater than the threshold value at step 360, it can be inferred that basket 120 is rubbing against or striking tub 114. Similar problems can also be detected at step 360 if the slope of the average power delivered to motor 128 is greater than the threshold value.

At step 370, controller 180 determines whether a predetermined time interval has elapsed and, e.g., whether the slope of the filtered power delivered to motor 128 exceeds the threshold value during the time interval. The predetermined time interval can be any suitable time interval at step 370. As an example, the predetermined time interval may be about eight seconds. The predetermined time interval can be selected in order to avoid responding to false or fleeting tub strikes or any other action that causes the slope of the filtered power delivered to motor 128 to be greater than the threshold value for a short period of time. Thus, the predetermined time interval can be selected in order to insure that basket 120 is rubbing or striking tub 114 during rotation of basket 120 within tub 114.

Controller 180 activates a fault mode of washing machine appliance 100, e.g., and deactivates motor 128 or washing machine appliance 100, at step 380 if the predetermined time interval has elapsed and the slope of the filtered power delivered to motor 128 exceeds the threshold value during the time interval at step 370. Thus, controller 180 can deactivate motor 128 or washing machine appliance 100 at step 380 if basket 120 is rubbing or striking tub 114 during rotation of basket 120 within tub 114. As another example, controller 180 can reduce the target speed of motor 128 below the threshold speed at step 380. It should be understood that controller 180 can take any suitable corrective or mitigating action at step 380 to avoid or limit damage to washing machine appliance 100 due to basket 120 rubbing or striking tub 114. In such a manner, method 300 can assist with avoiding or limiting damage to washing machine appliance 100 due to basket 120 rubbing or striking tub 114 during rotation of basket 120 within tub 114.

FIG. 4 illustrates exemplary plots of wash cycles with fault and no fault loads. In FIG. 4, controller 180 utilizes method 300 to activate a fault mode of washing machine appliance 100 when basket 120 rubs or strikes tub 114 during rotation of basket 120 within tub 114. As may be seen in FIG. 4, controller 180 operates motor 128 such that a target speed of basket 120 is about one thousand two hundred and fifty revolutions per minute for both wash cycles, and controller 180 also operates motor 128 such that the speed of basket 120 increases at a substantially constant acceleration rate until basket 120 is rotating at the target speed.

During the no fault wash cycle, a power slope (e.g., the slope of the average power delivered to motor 128) is substantially constant between about twenty seconds and about three minutes twenty seconds. Thus, controller 180 does not activate the fault mode of washing machine appliance 100 during the no fault wash cycle. Conversely, the power slope increases dramatically during the fault wash cycle at about one minute twenty seconds. Thus, controller 180 activates the fault mode of washing machine appliance 100 during the fault wash cycle because basket 120 may be rubbing or striking tub 114 during rotation of basket 120 within tub 114.

FIG. 5 illustrates a method 500 for operating a washing machine appliance according to another exemplary embodiment of the present subject matter. Method 500 can be used to operate any suitable washing machine appliance, such as washing machine appliance 100 (FIG. 1). Controller 180 of washing machine appliance 100 may be programmed or utilized to implement method 500. As discussed in greater detail below, method 500 can assist with detecting striking of tub 114 with basket 120 during rotation of basket 120 within tub 114.

At step 510, basket 120 is rotated at a first angular velocity with motor 128. As an example, controller 180 can operate motor 128 such that motor 128 rotates basket 120 at the first angular velocity. At step 520, a power delivered to motor 128 at step 510 is determined In particular, an average power delivered to motor 128 at step 510 may be determined at step 520. The average power may be determined over a window, such as an eight second window. As an example, controller 180 can determine the power delivered to motor 128 at step 510 during step 520.

At step 530, basket 120 is rotated at a second angular velocity with motor 128. As an example, controller 180 can operate motor 128 such that motor 128 rotates basket 120 at the second angular velocity. At step 540, a power delivered to motor 128 at step 530 is determined In particular, an average power delivered to motor 128 at step 530 may be determined at step 540. The average power may be determined over a window, such as an eight second window. As an example, controller 180 can determine the power delivered to motor 128 at step 530 during step 540.

The first and second angular velocities can be any suitable angular velocities. In certain exemplary embodiments, the first angular velocity is less than the second angular velocity. As an example, the first angular velocity may be greater than about one hundred radians per second (e.g., about one thousand revolutions per minute).

At step 550, a change in the power delivered to motor 128 over time is calculated based at least in part on the power delivered to motor 128 at step 510 and the power delivered to motor 128 at step 530. Controller 180 can calculate the change in the power delivered to motor 128 over time at step 550. At step 560, controller 180 establishes whether the change in the power delivered to the motor 128 over time exceeds a threshold value. The threshold value can be any suitable value. In particular, the threshold value can be selected in order permit controller 180 to detect basket 120 rubbing or striking tub 114 during rotation of basket 120 within tub 114. For example, if the change in the power delivered to motor 128 over time is greater than the threshold value at step 560, it can be inferred that basket 120 is rubbing against or striking tub 114. Similar problems can also be detected at step 560 if the change in the power delivered to motor 128 over time is greater than the threshold value. Steps 510, 520, 530, 540, 550 and 560 can be repeated while motor 128 is accelerating drum 120 to a target speed in order to permit or assist controller 180 with detecting basket 120 rubbing or striking tub 114 while motor 128 is accelerating drum 120 to the target speed.

Method 500 can also include monitoring the power delivered to motor 128 at step 510 and the power delivered to motor 128 at step 530. In particular, controller 180 can monitor the power delivered to motor 128 at step 510 and the power delivered to motor 128 at step 530 in order to determine whether the power delivered to motor 128 at steps 510 and/or 530 exceeds a threshold power.

The threshold power can be any suitable power. As an example, the threshold power may be about seven hundred Watts. The threshold power can be selected in order permit controller 180 to detect faults or errors during operation of washing machine appliance 100. For example, if the power delivered to motor 128 at steps 510 and/or 530 is greater than the threshold power, a clothing article could be lodged between tub 114 and basket 120 such that rotation of basket 120 within tub 114 is hindered. Similar problems can also be detected if the power delivered to motor 128 at steps 510 and/or 530 is greater than the threshold power.

Method 500 can further include activating a fault mode of washing machine appliance 100. In particular, controller 180 can activate the fault mode of washing machine appliance 100 and, e.g., deactivate motor 128 or washing machine appliance 100, if the power delivered to motor 128 at steps 510 and/or 530 is greater than the threshold power. Similarly, controller 180 can activate the fault mode of washing machine appliance 100 if the change in the power delivered to the motor 128 over time exceeds the threshold value. In such a manner, method 500 can assist with limiting or reducing damage to washing machine appliance 100, e.g., when washing machine appliance 100 is improperly loaded or malfunctioning.

FIG. 6 illustrates a method 600 for operating a washing machine appliance according to an additional exemplary embodiment of the present subject matter. Method 600 can be used to operate any suitable washing machine appliance, such as washing machine appliance 100 (FIG. 1). Controller 180 of washing machine appliance 100 may be programmed or utilized to implement method 600. As discussed in greater detail below, method 600 can assist with detecting striking of tub 114 with basket 120 during rotation of basket 120 within tub 114.

At step 610, basket 120 is spun with motor 128. As an example, controller 180 can activate or operate motor 128 at step 610 in order to spin basket 120 within tub 114. At step 620, an angular velocity of basket 120 is increased at a first acceleration rate during step 610. As an example, controller 180 can operate motor 128 such that motor 128 increases the angular velocity of basket 128 at the first acceleration rate during step 620. At step 630, the angular velocity of basket 120 is increased at a second acceleration rate after step 620. As an example, controller 180 can operate motor 128 such that motor 128 increases the angular velocity of basket 120 at the second acceleration rate during step 630. In particular, controller 180 can operate motor 128 such that motor 128 increases the angular velocity of basket 120 at the first acceleration rate until the angular velocity of basket 120 exceeds a threshold angular velocity, e.g., about one hundred radians per second (or about one thousand revolutions per minute) or about ninety four radians per second (or about nine hundred revolutions per minute).

The first and second acceleration rates can be any suitable acceleration rates. In certain exemplary embodiments, the first acceleration rate is greater than the second acceleration rate. For example, the first acceleration rate may be about one radian per second squared (or about ten revolutions per minute per second). As another example, the second acceleration rate may be about two-tenths of a radian per second squared (or about two revolutions per minute per second). The second acceleration rate can be selected in order permit controller 180 to detect basket 120 rubbing or striking tub 114 during rotation of basket 120 within tub 114 as discussed in greater detail below. As an example, by accelerating basket 120 slowly during step 630, power delivered to motor 128 can remain substantially constant such that it can be inferred that changes in power deliver to motor 128 are attributable to basket 120 striking tub 116.

At step 640, an average power delivered to motor 128 during step 630 is determined In certain exemplary embodiments, the average power delivered to motor 128 is a rolling average power delivered to motor 128 during a window. The window can be any suitable time period. For example, the window may be about eight seconds. Controller 180 can determine the average power delivered to motor 128 during step 630 at step 640.

At step 650, a slope of the average power delivered to motor 128 is established. As an example, controller 180 can determine or establish the slope of the average power delivered to motor 128 based at least in part on the average power delivered to motor 128 determined at step 640. At step 660, the slope of the average power delivered to motor 128 is monitored. Controller 180 can monitor the slope of the average power delivered to motor 128 at step 660 in order to establish if the slope of the average power delivered to motor 128 exceeds a threshold value.

The threshold value can be any suitable value. In particular, the threshold value can be selected in order permit controller 180 to detect basket 120 rubbing or striking tub 114 during rotation of basket 120 within tub 114. For example, if the slope of the average power delivered to motor 128 is greater than the threshold value at step 660, it can be inferred that basket 120 is rubbing against or striking tub 114. Similar problems can also be detected at step 660 if the slope of the average power delivered to motor 128 is greater than the threshold value.

Method 600 can also include activating a fault mode of washing machine appliance 100. In particular, controller 180 can activate the fault mode of washing machine appliance 100 and, e.g., deactivate motor 128 or washing machine appliance 100, if the slope of the average power delivered to motor 128 at steps 630 is greater than the threshold value. In such a manner, method 600 can assist with limiting or reducing damage to washing machine appliance 100, e.g., when washing machine appliance 100 is improperly loaded or malfunctioning.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A method for operating a washing machine appliance, the washing machine having a drum rotatably mounted within a tub, the washing machine appliance also having a motor configured for selectively rotating the drum within the tub, the method comprising: rotating the drum at a first angular velocity with the motor; determining a power delivered to the motor at said step of rotating the drum at the first angular velocity; rotating the drum at a second angular velocity with the motor; determining the power delivered to the motor at said step of rotating the drum at the second angular velocity; calculating a change in the power delivered to the motor over time based at least in part on the power delivered to the motor at said step of rotating the drum at the first angular velocity and the power delivered to the motor at said step of rotating the drum at the second angular velocity; and establishing whether the change in the power delivered to the motor over time exceeds a threshold value.
 2. The method of claim 1, wherein the first angular velocity is less than the second angular velocity.
 3. The method of claim 2, wherein the first angular velocity is greater than about one hundred radians per second.
 4. The method of claim 1, wherein said step of determining the power delivered to the motor at said step of rotating the drum at the first angular velocity comprises determining an average power delivered to the motor at said step of rotating the drum at the first angular velocity, and said step of determining the power delivered to the motor at said step of rotating the drum at the second angular velocity comprises determining an average power delivered to the motor at said step of rotating the drum at the second angular velocity.
 5. The method of claim 1, further comprising monitoring the power delivered to the motor at said step of rotating the drum at the first angular velocity and the power delivered to the motor at said step of rotating the drum at the second angular velocity in order to determine whether the power delivered to the motor exceeds a threshold power.
 6. The method of claim 5, wherein the threshold power is about seven hundred watts.
 7. The method of claim 5, further comprising activating a fault mode of the washing machine appliance if the change in the power delivered to the motor over time exceeds the threshold value or if the power delivered to the motor exceeds the threshold power.
 8. The method of claim 1, further comprising repeating said steps of rotating the drum at the first angular velocity, determining the power delivered to the motor at said step of rotating the drum at the first angular velocity, rotating the drum at the second angular velocity, determining the power delivered to the motor at said step of rotating the drum at the second angular velocity, calculating the change in the power delivered to the motor over time and establishing whether the change in the power delivered to the motor over time exceeds the threshold value while the motor is accelerating the drum to a target speed.
 9. A method for operating a washing machine appliance, the washing machine having a drum rotatably mounted within a tub, the washing machine appliance also having a motor configured for selectively rotating the drum within the tub, the method comprising: spinning the drum with the motor; increasing an angular velocity of the drum at a first acceleration rate during said step of spinning; increasing the angular velocity of the drum at a second acceleration rate after said step of increasing the angular velocity of the drum at the first acceleration rate; determining an average power delivered to the motor during said step of increasing the angular velocity of the drum at the second acceleration rate; establishing a slope of the average power delivered to the motor; and monitoring the slope of the average power delivered to the motor in order to establish if the slope of the average power delivered to the motor exceeds a threshold value.
 10. The method of claim 9, wherein the first acceleration rate is greater than the second acceleration rate.
 11. The method of claim 10, wherein the first acceleration rate is about one radian per second squared.
 12. The method of claim 10, wherein the second acceleration rate is about two-tenths of a radian per second squared.
 13. The method of claim 9, wherein the average power delivered to the motor comprises a rolling average power delivered to the motor during a window, the window being about eight seconds.
 14. The method of claim 9, wherein said step of increasing the angular velocity of the drum at the first acceleration rate comprises increasing the angular velocity of the drum at the first acceleration rate until the angular velocity of the drum exceeds a threshold velocity.
 15. The method of claim 14, wherein the threshold velocity is greater than about ninety radians per second.
 16. The method of claim 9, further comprising monitoring the average power delivered to the motor during said step of monitoring the slope of the average power delivered to the motor in order to determine whether the average power delivered to the motor exceeds a threshold power.
 17. The method of claim 16, wherein the threshold power is about seven hundred watts.
 18. The method of claim 16, further comprising activating a fault mode of the washing machine appliance if the slope of the average power delivered to the motor exceeds the threshold value at said step of monitoring the slope of the average power delivered to the motor or if the average power delivered to the motor exceeds the threshold power at said step of monitoring the average power delivered to the motor.
 19. A washing machine appliance, comprising: a cabinet; a tub positioned within the cabinet; a drum rotatably mounted within the tub, the drum defining a wash chamber for receipt of articles for washing; a motor in mechanical communication with the drum, the motor configured for selectively rotating the drum within the tub; and a controller in operative communication with the motor, the controller configured for rotating the drum at a first angular velocity with the motor; determining a power delivered to the motor at said step of rotating the drum at the first angular velocity; rotating the drum at a second angular velocity with the motor; determining the power delivered to the motor at said step of rotating the drum at the second angular velocity; calculating a change in the power delivered to the motor over time based at least in part on the power delivered to the motor at said step of rotating the drum at the first angular velocity and the power delivered to the motor at said step of rotating the drum at the second angular velocity; and establishing whether the change in the power delivered to the motor over time exceeds a threshold value.
 20. The washing machine appliance of claim 19, wherein the controller is further configured for repeating said steps of rotating the drum at the first angular velocity, determining the power delivered to the motor at said step of rotating the drum at the first angular velocity, rotating the drum at the second angular velocity, determining the power delivered to the motor at said step of rotating the drum at the second angular velocity, calculating the change in the power delivered to the motor over time and establishing whether the change in the power delivered to the motor over time exceeds the threshold value while the motor is accelerating the drum to a target speed. 